The present invention relates to an electromagnetic clutch having a solenoid coil, a coil housing disposed surrounding the solenoid coil, an armature plate disposed facing the side of the coil housing, and a clutch mechanism, and more particularly relates to a lubricating structure for supplying lubricating oil to the area where the coil housing faces the armature plate (facing gap)
Various electromagnetic clutches of this type were known in the past, and have been disclosed in Japanese Laid-Open Patent Applications H10-194004 and 2000-240685 and elsewhere. The electromagnetic clutches disclosed in these publications are used as differential mechanisms in automobile axles. For instance, in Japanese Laid-Open Patent Application H10-194004, differential clutch mechanisms each composed of an electromagnetic clutch are installed on the left and right of a final reduction mechanism consisting of hypoid gears in a rear axle device, and a differential action is achieved and drive is switched between two- and four-wheel-drive modes by engaging and disengaging these left and right differential clutch mechanisms.
This differential clutch mechanism comprises a wet-type multi-plate clutch mechanism, a solenoid mechanism, and a ball cam mechanism. The solenoid mechanism comprises an armature plate facing a coil housing provided around a solenoid coil, the armature plate is linked to the input side of the clutch mechanism, and the coil housing is linked to one end of the ball cam mechanism. The other end of the ball cam mechanism is linked to the output side of the clutch mechanism and provides a thrust force for engaging the clutch mechanism.
With this differential clutch mechanism, current is sent to the solenoid coil to generate a magnetic force which clamps the armature plate to the coil housing, and this causes the coil housing to rotate along with the armature plate, so that one end of the ball cam mechanism rotates along with the input side of the clutch mechanism. Because the other (second) end of the ball cam mechanism here is linked to the output side of the clutch mechanism, if there is a rotational difference between the input and output of the clutch mechanism (such as when the rear wheel rotation is different with respect to the rotation on the axle drive side), the second end will be rotationally driven with respect to the first end of the ball cam mechanism, a thrust force in the engagement direction will be imparted from the second end to the clutch mechanism, and the differential clutch mechanism will be engaged.
A problem with a conventional differential clutch mechanism, however, was that when the clamping of the armature plate to the coil housing was controlled by means of the magnetic force of the solenoid, noise resulted when the two metal components came into sliding contact, and on/off control was virtually the only control that was possible. Consequently, the engagement of the differential clutch mechanisms could only be controlled in an on/off fashion, and controlling partial engagement was exceedingly difficult.
It is an object of the present invention to allow control so that not only complete engagement of the coil housing and armature plate is possible in an electromagnetic clutch, but also partial engagement in which the two components are in sliding contact.
In the present invention, an electromagnetic clutch has a solenoid coil, a coil housing disposed surrounding the solenoid coil, an armature plate disposed facing the side of the coil housing, and a clutch mechanism (in an embodiment, for example, a mechanism comprising a clutch housing 52, separator plates 53, clutch plates 54, a pressure plate 55, and so forth), the current flowing to the solenoid coil is controlled so as to control the clamping of the armature plate to the coil housing, and the clamping force acting on the armature plate is used to control the engagement of the clutch mechanism. Furthermore, there is provided a lubricating oil supply channel for supplying lubricating oil from the inside in the radial direction into a gap between the coil housing and the armature plate (such as a first lubricating hole 61 and a third lubricating hole 63 in the embodiments), and an oil reservoir holding lubricating oil to be supplied into the gap is formed around the inner periphery of the portion where the coil housing faces the armature plate.
With an electromagnetic clutch lubricating structure such as this, the lubricating oil held in the oil reservoir is adequately and effectively supplied into the gap where the coil housing faces the armature plate, which affords control over the two components such that they are in smooth sliding contact without making any noise. Accordingly, the clutch mechanism not only can be controlled in on/off fashion, but can also easily be controlled for partial engagement.
It is preferable in the above structure if an oil fence ring is mounted around the inner peripheral surface of the armature plate, and the lubricating oil supplied from the lubricating oil supply channel is held back by this oil fence ring, forming the oil reservoir. In this case, it is preferable if an annular rubber lip is provided at the inner peripheral end of the oil fence ring.
It is also preferable in the above structure if at least part of the inner peripheral end of the armature plate projects annularly toward the inside, forming an annular projection, and the lubricating oil supplied from the lubricating oil supply channel is held back by this annular projection, forming the oil reservoir.
Further, in the present invention, an electromagnetic clutch has a solenoid coil, a coil housing disposed surrounding the solenoid coil, an armature plate disposed facing the side of the coil housing, and a clutch mechanism, and there is provided a cam mechanism (such as a ball cam mechanism 65 in the embodiments) that controls the current flowing to the solenoid coil so as to control the clamping of the armature plate to the coil housing, and converts the clamping force acting on the armature plate into the engagement force of the clutch mechanism, thereby constituting a power transmission apparatus. In this case, the clamping force acting on the armature plate is used via the cam mechanism to control the engagement of the clutch mechanism, there is provided a lubricating oil supply channel for supplying lubricating oil from the inside in the radial direction into a gap between the coil housing and the armature plate, and an oil reservoir holding lubricating oil to be supplied into the gap is formed around the inner periphery of the portion where the coil housing faces the armature plate.
Again with an electromagnetic clutch lubricating structure such as this, the lubricating oil held in the oil reservoir is adequately and effectively supplied into the gap where the coil housing faces the armature plate, which affords control over the two components such that they are in smooth sliding contact without making any noise. Accordingly, the clutch mechanism not only can be controlled in on/off fashion, but can also easily be controlled for partial engagement.
It is preferable in the above structure if the lubricating oil supply channel is formed through the cam mechanism, so that the cam mechanism will also be thoroughly lubricated.
It is preferable in the above structure if an oil fence ring is mounted around the inner peripheral surface of the armature plate, and the lubricating oil supplied from the lubricating oil supply channel is held back by this oil fence ring, forming the oil reservoir. In this case, it is preferable if an annular rubber lip is provided at the inner peripheral end of the oil fence ring.
Also, at least part of the inner peripheral end of the armature plate may project annularly toward the inside, forming an annular projection, and the lubricating oil supplied from the lubricating oil supply channel may be held back by this annular projection, forming the oil reservoir.
The above-mentioned cam mechanism can comprise a first cam plate linked to the coil housing, a second cam plate that is linked to the output-side member of the clutch mechanism and imparts an engagement thrust force to the clutch, and cam balls that are disposed in cam grooves formed in the first and second cam plates and are sandwiched between the first and second cam plates. In this case, it is preferable if the lubricating oil supplied from the lubricating oil supply channel is held back by an oil seal mounted on the inner peripheral surface of the coil housing and having a lip facing the side of the first cam plate, forming the oil reservoir.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.